Lightweight gypsum panel

ABSTRACT

GYPSUM WALLBOARD IN WHICH ABOUT HALF THE VOLUME OF THE CORE CONSISTS OF VERY LIGHTWEIGHT PARTICLES FORMED BY TEARING FOAMED POLYSTYRENE BEADS INTO A SHREDDED FORM.

Oct. 10, 1972 HARLQCK EIAL 3,697,366

LIGHTWEIGHT GYPSUM iANEL Filed April 13, 1970 ska- INVENTORS George H.Hurloc'k Ed we rd A. Burke rd wwzzm ATTORNEY Patented Oct. 10, 19723,697,366 LIGHTWEIGHT GYPSUM PANEL George H. Harlock and Edward A.Burkard, East Amherst, N.Y., assignors to National Gypsum Company,Buffalo, N.Y.

Filed Apr. 13, 1970, Ser. No. 27,755 Int. Cl. 83% 13/00 US. Cl. 161-159Claims ABSTRACT OF THE DISCLOSURE Gypsum wallboard in which about halfthe volume of the core consists of very lightweight particles formed bytearing foamed polystyrene beads into a shredded form.

This invention relates to a lightweight gypsum wallboard having asubstantial portion of lightweight aggregate consisting of shreddedpolystyrene beads.

Several types of lightweight aggregate have been tried, somesuccessfully and some unsuccessfully, in forming the core of gypsumwallboard. The most common means for providing a lower density of theset gypsum core involves the use of a soap to produce a foam whichresults in a multitude of voids throughout the core. Various problemshave presented themselves with regard to the use of various lightweightaggregates. There are practical limits to how low the density can be forany aggregate, without effectively destroying the integrity of theaggregate. Inability of some aggregates to adhere to the gypsum matrixcan result in inadequate core integrity. Cost of an aggregate canoutweigh its advantages.

It is an object of the present invention to provide an improvedlightweight gypsum board. It is a further object to provide a novel coreformulation of set gypsum and lightweight aggregate.

Briefly, the present invention provides a lightweight gypsum boardhaving an aggregate formed by shredding low density polystyrene beads.

These and other objects and advantages of the invention will be morereadily apparent when considered in relation to the preferredembodiments as set forth in the specification and shown in the drawingsin which:

FIG. 1 is a perspective view of a paper covered gypsum wallboardembodying the present invention.

FIG. 2 is an enlarged end view of a portion of the gypsum Wallboard ofFIG. 1.

FIG. 3 is an elevational view illustrating, in enlarged form, particlesof low density shredded plastic foam aggregate.

Referring to FIG. 1 there is shown a gypsum Wallboard 10 consisting of acore 12 enclosed with a face paper 14, which extends across thewallboard face 16 and completely around each edge 18, and a back paper20 which extends almost across the wallboard back 22. Face paper 14 hasedges 24 extending onto the wallboard back 22. Edges 26 of back paper 20overlap the edges 24 of face paper 14.

Each wallboard edge 18 is of tapered form for use in drywallconstruction with well known joint-concealing systems; however, theinvention is suited for wallboards having a square edge. bevelled edgeor round edge.

'allboard 10 is preferably made on well known con tinuous machines forproducing gypsum wallboard of all kinds, wherein face paper 14, incontinuous form, is disposed on a continuous conveyor. :1 water slurryof the settable gypsum core material is disposed on the face paper, backpaper 20. in continuous form. is disposed on the slurry, the edges 24 ofthe face paper are folded up and over the edges 26 of the back paper,the settable gypsum core material hardens, the continuous hardened boardis cut into desired length boards 10 and the boards 10 are dried.

The paper may be of the type commonly employed for gypsum boards, suchas relatively high quality cream face paper for face paper 14 and agreyback grade of paper for back paper 20. These papers are commonlymade on a cylinder type paper-making machine wherein about six to tenplies are combined to form a unitary paper sheet of about .020 inchthickness. The creamface type paper dilfers from the greyback in thatthe top ply or top two plies of creamface consist of a lighter coloredpulp stock, forming a cream-colored outer surface on the wallboard face16.

FIG. 2 is an enlarged view of the end of wallboard 10, showing thecombination in the core 12 of shredded plastic foam fragments 30, and acontinuous matrix therebetween of set gypsum 32. The composition of thecore of wallboard 10, containing these very lightweight fragments 30,produces a very lightweight wallboard.

EXAMPLE I A formulation of core 12 that has been found highlyadvantageous in accordance with the invention, based on 1000 sq. ft., ofV2 inch wallboard, is as follows:

Lbs.

'Settable gypsum 946 Water of rehydration 123 Starch 9.33

Pulp 7.2 Set Gypsum Accelerator l2 Shredded plastic foam 1 8.3 Soap 17Core weight 1106.00 Face and back paper 144.00

Wallboard weight 1250.00

1 .3 lb./eu. ft.

As is well known in wallboard manufacture, there will also be needed anadditional amount of water to provide the desired consistency duringforming of the core, which excess water is evaporated off in the dryingstep.

EXAMPLE II An even lighter wallboard has been satisfactorily producedwith the following core formulation:

Lbs.

Settable gypsum 915.8 Water of rehydration 119.1 Starch 8.93 Set gypsumaccelerator l3 Shredded plastic foam 1 S Soap .17

Core weight 1065.00 Face and back paper 144.00

Wallboard weight 1209.00

.3 lb./cu. ft.

Waste newspaper pulp, a common ingredient in wallboard, has been omittedin Example II. A second difference, essentially unrelated to theomission of the pulp, is the lighter weight, which resulted from adifferent mixing of the wet ingredients avoiding breaking down as muchof the soap-produced foam in the mix. The pulp in Example I may havelessened the stability of the soap-produced foam to some extent.

. Although determining variability in accordance with the inventionwould require endless evaluation, it is contemplated that at least thefollowing ranges of ingredients is possible:

Settable gypsum lbs 900-1200 Water of rehydration -lbs As requiredStarch 6l4 Pulp lbs 14 Accelerator lbs As required Shredded plastic foamcu. ft Up to 35 The shredded plastic foam is preferably the product ofshredding expanded polystyrene beads. Shredding is to be understood asdistinctly different from a severing which produces a clean or smoothsurface. It is essential, in accordance with the invention that theshredded plastic foam be small particles which are produced in a waywhich produces an extremely uneven surface,

One suitable method for producing the critical shredded rough surface isdisclosed in US. Pat. 3,338,848 to be by a hammer mill, and since thefragmented particles which are described therein are equivalent to thecritical shred ded plastic foam of the present invention, referencethereto can assist in understanding the present invention.

The expanded polystyrene beads may be ellipsoids with a major diameterof about A to /2 inch and a density of about .3 to about 1.0 lb./cu. ft,preferably about .3 lb./ cu. ft. After shredding the beads, the densityof the shredded material should be about the same as the bead densityand the shredded particles will mostly be of a size of about V to /4inch.

In FIG. 3, two shredded plastic foam fragments 30 are shown, enlarged,to give an idea of the randomness and roughness of the shape, whichpermits settable gypsum to form crystals which penetrate the fragmentsand become firmly bonded thereto, in the setting of the gypsum boardcore 12.

Wallboards made in accordance with the invention have a central castgypsum core of unusual strength and in tegrity, in many respects equalto the characteristics of the present standard gypsum board cores whichaverage about 50% higher weight.

As can be seen in FIG. 2, the surface of the central cast gypsum coreconforms smoothly to the paper and has a surface formation which isindependent of the shape of the fragments 30 embedded within the cast,or, in this example, the wallboard core.

The formulations of the invention permit ease of manufacture of gypsumwallboard and result in improved drying characteristics, permittingfaster drying and less heat requirement relative to standard wallboard.Warehousing and shipping costs are reduced since larger units, of equalweight, can be handled.

Having completed a detailed disclosure of the preferred embodiments ofthe invention, so that others may practice the same, we contemplate thatvariations may be made without departing from the essence of theinvention.

We claim:

1. The method of making gypsum wallboard comprising the steps of forminglightweight expanded cellular plastic beads having a major diameter ofabout A to V;

inch and a density of about 0.3 to 1.0 lb./cu. ft., shredding said beadsinto lightweight fragments of a size of about ,5 to 4 inch having highlyuneven, rough exterior surfaces, mixing said shredded fragments with anaqueous settable gypsum slurry, placing said slurry between a face paperand a back paper to form a wallboard, the solids content of said slurrycomprising a major portion of gypsum binder, and allowing said slurry toset and dry with said fragments embedded within said slurry between saidface paper and said back paper, thus resulting in a very lightweight,strong gypsum core.

2. The method of claim 1, wherein said beads are formed of polystyrene.

3. The method of claim I wherein said set and dried wallboard has anominal weight of about 1200 pounds per thousand square feet, per halfinch thickness.

4. The method of claim 1 wherein said shredded fragments are aboutone-half the dry volume of said wallboard.

5. A set gypsum cast containing a lightweight aggregate and a majorportion of weight of set gypsum binder, said aggregate consisting ofshredded particles of low density cellular plastic, said particleshaving highly uneven, rough exterior surfaces, said set gypsum forming asubstantially continuous binder matrix extending about and into saidrough surfaces of said shredded particles, said cast having an exteriorsurface formation which is substantially independent of the shape ofsaid particles.

6. A set gypsum cast as defined in claim 5, wherein said low densitycellular plastic particles are shredded polystyrene beads of about 0.3to 1.0 lbs. per cu. ft.

7. A lightweight gypsum wallboard having a central core disposed betweena face paper and a back paper, said central core consisting of a setgypsum cast as defined in claim 5.

8. A lightweight gypsum wallboard as defined in claim 7 wherein said lowdensity cellular plastic particles are shredded polystyrene beads ofabout 0.3 to 1.0 lbs. per cu. ft.

9. A lightweight gypsum wallboard as defined in claim 8 wherein saidparticles are of a size of about to A inch.

10. A lightweight gypsum wallboard as defined in claim 8 wherein saidparticles are about half the volume of said central core.

References Cited UNITED STATES PATENTS 2,009,146 7/[935 New l06-ll02,366,673 l/l945 Paley lO6ll0 3,257,338 6/l966 Sefton 2602.5 B 3,338,8488/1967 Hamilton 260-25 B 3 462,34l 8/1969 Littin l5642 MORRIS SUSSMAN,Primary Examiner Notice of Adverse Decision in Interference InInterference No. 99,139, involving Patent No. 3,697,366, G. H. Harlockand E. A. Burkard, LIGHTWEIGHT GYPSUM PANEL, final judgment adverse tothe patentees was rendered Oct. 29, 197 6, as to claim 1.

[Ofiicz'al Gazette February 1, 1.977.]

